1. Technical Field
The present application relates to a wavelength conversion element including phosphor particles and a method of manufacturing she some, and an LED element and a semiconductor laser light emitting device using the same.
2. Description of the Related Art
In recent years, a light emitting diode (LED) has come into use for lighting, and a higher-brightness and longer-life LED is desired to be developed. Conventionally, a wavelength conversion element including a phosphor layer for a white LED is forced by curing a resin mixture in which phosphor particles are mired with a silicone resin or the like. However, when a large current is passed through a high-brightness LED chip which is commercialized in recent years, the silicone resin is liable to be deteriorated by heat and high-brightness ultraviolet radiation generated from the LED chip. Therefore, as a matrix for forming a phosphor layer in which phosphor particles are dispersed, a matrix using not an organic substance such as a silicone resin which is liable to toe deteriorated by heat and ultraviolet radiation but an inorganic substance which is less liable to be deteriorated by heat and ultraviolet radiation is required to be realized.
International Patent Publication No. 2011/111293 discloses a phosphor layer in which, in order to improve the resistance to heat and the resistance to ultraviolet radiation of a silicone resin, phosphor particles carrying cerium oxide as a heat-resistant material are dispersed in the silicone resin.
Japanese Patent Translation Publication No. 2011-503266 (in particular, paragraph 0002) describes that a phosphor for an LED such as an yttrium aluminum garnet (YAG) phosphor or a terbium aluminum garnet (TAG) phosphor has a high refractive index of 1.7 or more, and that, in an LED, ordinarily, the phosphor is embedded in a silicone resin having a refractive index of 1.4 to form a phosphor layer, and thus, due to the refractive index difference (0.4) between the refractive index of the phosphor (1.8) and the refractive index of the silicone resin (1.4), a considerable ratio of light is scattered at an interface between the phosphor and the resin in the phosphor layer.
Japanese Patent Application Laid-Open Publication No. 2011-168627 (in particular, paragraph 0028 and paragraph 0032) discloses a technology in which, after a phosphor particle layer is formed on a substrate from a solution in which phosphor particles sire dispersed using electrophoresis, a light-transmitting substance to be an inorganic substance matrix is filled in voids in the phosphor particle layer using a sol-gel method. It is disclosed that the light-transmitting substance is preferably glass, and is a substance which is in a glass state and transmits light. Further, as combinations of phosphor particles and an inorganic matrix, examples such as a Ca-αSiAlON:Eu phosphor (refractive index 1.95 and silica (refractive index 1.45), a YAG phosphor (refractive index 1.8) and zinc oxide (refractive index 1.95) are disclosed.
Japanese Patent Application Lard-Open Publication No. 2008-66365 (in particular, paragraph 0003) discloses that, when a cavity in which phosphor particles and a light-transmitting material to be a matrix do not exist is caused in a phosphor layer, the existence of such a cavity attenuates light from the LED and light from the phosphor.
Japanese Patent Application Laid-Open Publication No. 2011-111506 (in particular, paragraph 0027) discloses that the refractive index of a phosphor whose composition is CaAiSiN3:Eu2+ is 2.0 and the refractive index of a phosphor whose composition is CaSc2O4:Ce3+ is 1.9.
Non-Patent Document, Hiroyo Segawa et. al., Opt. Mater. 33 (2010) 170, discloses that SiAlON which is popularly used as phosphor particles in an LED has a refractive index in a range of 1.855 to 1.897 depending on the composition thereof.